The best thing that I've found for mashing is single-speed mtb. It's kinda like the downhill drill, but on a mtb. Since you only have one speed, you are going to end up mashing up some hills, in which case you stand up, but you get a lot stronger and you learn to spin up the hills, and you spin spin spin spin fast down the downhills. Ss mtb's are great for power too

I have a fixie that I ride around school. I don't put many many miles on it, but it has DEFINITELY helped with efficiency too since you have no choice but to pedal.